Maybe it’s a good thing Roger Federer didn’t make it to Wednesday night’s U.S. Open quarterfinal bash. It might have been ugly.

Instead, Tommy Robredo, who knocked Federer out of the Open in the fourth round, became the sacrificial lamb and the Rafael Nadal rampage continued on in a thumping of his fellow Spaniard.

Nadal lost just five points in the first set, won the match’s first eight games and posted a 6-0, 6-2, 6-2 drubbing of Robredo to advance to the semifinals. The match was over in a tidy one hour, 40 minutes and the Ashe Stadium crowd cheered on Robredo at several junctures out of pity.

“I think I played great the first set,’’ Nadal said. “It’s my first set so far this year 100 percent. It was my best match of the tournament.”

The celebrities were out at Ashe Stadium — Jimmy Buffet, Michael Strahan, Dakota Fanning, Vivica A. Fox, Jane Krakowski. They got tickets in hopes of seeing an historic, first-ever Federer-Nadal showdown in Flushing, but it never materialized, taking a lot of buzz out of the Open.

But maybe it was better this way. The last thing Federer’s fans want to see is him get embarrassed by his arch rival on Flushing Meadows who is playing out of his mind.

Nadal still hasn’t lost his serve in the tournament and is unbeaten on hardcourts this year (20–0) — historically his worst surface. Nadal, now 7-0 against Robredo, has held serve 67 straight times. Robredo didn’t even muster a break point and won just 53 percent of his first serves.

During the match, the bored Ashe crowd went crazy with the score 2-0 in the second set, Robredo already down a break but getting up 40-15 on his serve. Robredo ultimately held serve for his first game of the match as Nadal sprayed a forehand wide and the crowd exploded like the title had been won.

If Federer watched the match, the whole scene had to make him feel frustrated. He got mauled in straight sets to Robredo on Labor Day. Even Federer admitted if he couldn’t get a set off Robredo, he had no business facing Nadal the way the Spanish lefty is pounding the ball so crisply, free of knee pain.

One semifinal is set with Nadal against the Frenchman Richard Gasquet on Super Saturday. The other semifinal figures to be Andy Murray vs. Novak Djokovic, but they have to get through their quarterfinals today. Djokovic takes on Mikhail Youznhy and Murray faces Stanislas Wawrinka.

Gasquet — who outlasted No. 4 David Ferrer 6-3, 6-1, 4-6, 2-6, 6-3 in 3 hours, 23 minutes to advance to his second career Grand Slam semifinal — is 0-10 against Nadal, who looks like a favorite to win his second Open.

Gasquet remembers beating Nadal as a 13-year-old in an under-14 event.

“I saw it on YouTube, and I can see I’m winning against him, so I don’t believe it sometimes,’’ Gasquet said.

Gasquet credited his improved fitness for being able to tough out his second consecutive five-set match, after outlasting Milos Raonic on Monday.

“I think I work a lot physically,” he said. “[I] played 4 hours and 30 minutes against Raonic, but I knew I could play another big match. I was feeling not so tired this morning.”

“He played a very good [match],” Ferrer said. “He was good with his backhand and he served very [well] in important moments. Maybe in the first and second sets, I didn’t play so [well]. I was a little bit tired. I tried to do my best. I [fought] until the last ball, but in the fifth set, when he [broke], I played a very bad game, with three [errors].”